Tendon transfer surgery is a common procedure to treat paralysis or paresis resulting from spinal cord injury, cerebral palsy or other neurological disorders. The tendon of a functioning muscle, sometimes even a direct antagonist, is sewn into the tendon of the weakened muscle to improve motor function in the desired direction. The recovery of motor function from these procedures can be limited and learning new motor patterns can be difficult. It is therefore important to develop quantitative assessment tools to measure the success of surgical manipulation of the musculoskeletal system and to track the progress of rehabilitation of individuals with injury to the peripheral motor apparatus. One such approach is the measurement of limb stiffness using robotic technology. This approach can potentially detect changes in musculoskeletal organization such as occurs with tendon transfer or fasciotomy as well as changes in proprioceptive circuits in the spinal cord and brainstem resulting from neurological disease. Stiffness measurements will be made on the hindlimbs of decerebrate cats after tendon transfer, fasciotomy and muscle reinnervation in order to establish the relationship between the manipulation of the motor system and the emergent mechanical properties. These measurements will then be used to evaluate adaptations of the motor system to the manipulation after a survival period. This approach can be readily adapted for use with human subjects, and potentially constitutes a powerful diagnostic tool. Among the several possible reasons for a less than satisfactory outcome of tendon transfer surgery, and one that appears not to have been considered until now, is that the relationships between the natural patterns of activation of the muscle and the mechanical feedback from the muscle are altered. This mismatch, rather than contributing to the retraining of muscular activation patterns, could result in suppression or reorganization of proprioceptive circuits. The proposed experiments have been designed to test the hypothesis that the altered timing of sensory information could limit recovery of function following tendon transfer. These experiments will utilize measurements of limb stiffness as well as evaluations of individual proprioceptive pathways in decerebrate cats.